1. Field of the Invention
The present invention relates to a method for producing an optical waveguide which is widely used for optical communications, optical information processing and other general optics.
2. Description of the Related Art
Optical waveguides are incorporated in optical devices such as optical waveguide devices, optical integrated circuits and optical interconnection boards, and are widely used in the fields of optical communications, optical information processing and other general optics. Such an optical waveguide typically includes a core having a predetermined pattern and serving as a light passage, and an under-cladding layer and an over-cladding layer which cover the core (see, for example, JP-A-2005-173039). For production of the optical waveguide, the under-cladding layer, the core and the over-cladding layer are typically formed in this order in stacked relation on a substrate.
Photosensitive resins are typically used as materials for forming the under-cladding layer, the core and the over-cladding layer in predetermined patterns. For patterning each of the photosensitive resins, an exposure mask formed with an opening pattern corresponding to the predetermined pattern is positioned on the photosensitive resin, which is in turn exposed to radiation via the exposure mask. An unexposed portion of the photosensitive resin is dissolved away, whereby an exposed portion of the photosensitive resin has the predetermined pattern.
The positioning of the exposure mask is typically achieved by means of an optical sensor or the like with reference to an alignment mark formed on the substrate. Meanwhile, an optical waveguide device including a light emitting element embedded in its optical waveguide is now under consideration. In the optical waveguide device, the core and the over-cladding layer tend to have an increased thickness as compared with the conventional optical waveguide. In this case, it is difficult to visually or optically detect the alignment mark on the substrate in the positioning of the exposure mask, thereby reducing the positioning accuracy. Particularly, where the alignment mark and the under-cladding layer are formed of the same transparent material, it is more difficult to visually or optically detect the alignment mark.